Sweep generator using nonlinear sweeps



May 7, 1957 B. CUTLER ETAL swEEP GENERATOR USING NONLINEAR swEEPs Filed Feb. 9, 1953 mv QQ .I QN nul mw w w. QQ N H I l limited States lauern: t

SWEEP GENERATOR USING NONLINEAR SWEEPS Burton Cutler, Los Angeles, and George B. Crane, Redondo Beach, Calif., assignors to Gilfillan Bros. Inc., Los Angeles, Calif., a corporation of California Application February 9, 1953, Serial No. 335,786

9 Claims. (Cl. 250-27) The present invention relates to improved circuitry for supplying energy to a load wherein the current flows at a decreasing rate as a function of time; and, more specifically, relates to improved circuitry for supplying current to a deflection coil of `a cathode ray tube in the production of exponential or logarithmic sweeps of a cathode ray beam.

In general, the present invention involves apparatus for supplying energy to a deflection coil of a cathode ray tube in the production of logarithmic or exponential sweeps of the character shown in Figure 1 wherein such sweeps are produced by current flowing through the deflection coil, the current owing at a decreasing rate, either exponential or logarithmic in character. For this purpose, the deflection coil is serially connected in a circuit which includes a grid controlled tube, the deflection coil, and a special power supply which embodies important features of the present invention. The power supply is such that it supplies a relatively high voltage at the start of a cathode beam sweep, the magnitude of suchvoltage, however, decreasing continuously with time so that, at the end of the cathode beam sweep, the voltage is a The power supply involves a condenser which is charged through a resistance during the generation of the sweep. At the end of the sweep, the voltage on the anode of the aforementioned tube, during the flyback time, increases, and this increase in anode voltage is transferred to effect a substantial short-circuiting of the aforementioned resistance, whereby the condenser may assume a SubstantiallyV fully charged condition preparatory to the start of thenext cathode beam sweep. t

It is therefore an object of the present invention to provide improved circuitry for accomplishing the aforementionedfunctions, operation and result.

A specific object of the present invention is to provide an improved power supply useful in supplying a load which requires a current flowing at a decreasing rate.

Another object of the present invention is to provide improved circuitry allowing the use of a relatively small power amplier tube which is controlled to producethe aforementioned current owing at a decreasing rate.

Another object of the present invention is to provide an improved arrangement of this character in which the power dissipation in the power amplifier tube supplying the deflection coil is greatly minimized.

Another object of the present invention is to provide an improved arrangement of this character for minimizing space requirements and improving mechanical structure and reliability.

The features Vof the present invention which are believed to be novel are set forth with particularity in the appended claims. This invention itself, both as to its organization and manner of operation, together with further objects and advantages thereof, may be best understood by reference to the following description taken in connection with the accompanying drawings in which:

Figure 1 shows a presentation produced on the face of a cathode ray tube by supplying an increasing current 2,791,686 Patented May 7, 1957 to a deflection coil of the cathode ray tube at a decreasing rate in accordance with certain features of the present invention;

Figure 2 is a schematic representation of apparatus useful in practicing the present invention; and such apparatus embodies features of the present invention; and

Figure 3 shows different voltage and current wave forms useful in producing a linear sweep as well as for producing a nonlinear sweep in accordance with features of the present invention.

Referring to the drawings, Figure 1 shows a presentation on a cathode ray tube produced by cathode beam sweeps, each starting from a central origin point 0. The angular position of each sweep represents, for example, the azimuthal position of an antenna beam scanning through space, while the length of the sweeps represents range. A presentation of this character involving the use of nonlinear sweeps, as shown in Figure l, is described and claimed in the copending patent application of Homer G. Tasker et al., Serial No. 175,168, now Patent No. 2,737,654. This presentation is formed by sweeps which travel outwardly from the point 0 with ever decreasing speeds. To accomplish this result, the current owing through the deflection coil of the cathode ray tube increases at a decreasing rate.

Normally, in the production of linear sweeps, asindicated in Figure 3, a voltage wave EL is supplied to the deflection coil. This waveform is generally square or trapezoidal so that the current through the induction coil IL increases at a uniform rate represented by the straight inclined line. This follows from the following equation Thus, in generating linear sweeps, when the voltage is of substantially constant magnitude, the current changes at a uniform rate.

V Heretofore, in developing sweeps of the character illustrated in Figure =l, a power amplifier tube was serially connected with the deflection coil and a power supply producing a substantially uniform voltage. Such power amplifier tube was grid controlled and had control voltages of the character illustrated at 10 in Figure 2 applied to the control grid of the same. Such an arrangement required -a relatively large power amplifier tube because of the relatively 'large amounts of power required to be dissipated by the same upon the following considerations. Using a constant voltage power supply of, for example, 700`volts, at the beginning of a cathode beam sweep,

is yabout 450 volts and during the latter portion of the sweep it is approximately 75 volts. This means that there is approximately 625 volts across the final power :amplifier tube when it 4is drawing the maximum current, i. e., about 300 milliamperes. Thus, the power dissipation required for a power amplifier tube producing non- 'linear sweeps and using a voltage source which is substantially constant in magnitude, is much larger than that required for equivalent linear cathode beam sweeps. Thus, one feature of the present invention pertains to autom-atie reduction of the magnitude of the supply voltage during the formation of the sweeps to such an extent that the voltage drop across the power amplifier tube remains substantially constant during the sweep interval, thereby greatly reducing the power required to be dissipated in the final amplifier tube and allowing a `smaller agences plied voltage to such deflection coil of the character illustrated at EN in Figure 3.

In Figure 2, the deflection coil 1-2--of the cathode4 ray tube is connected in the anode current path of the nal power amplifier tube 13 which may be a tetrode or a beam power type tube. This series -circuit comprising the coil 12 and tube 13 is supplied from a voltage source which, for all intents and purposes, as will be more evident from the following description, may be considered to be the voltage developed across the condenser 15 having its ungrounded terminal connected to one terminal of the coil 12, the other termin-al of coil 12 being connected to the anode of tube 13 and the cathode of tube 13 being grounded. A voltage source 17 is connected between the lscreen grid and lcathode of tube 13, such source 17 being bypassed by bypass condenser 18.

The control grid of tube 13 is coupled to sweep-form.- `ing circuitry 20 which is of the character described in the aforementioned copending application Serial No. 175,168, for producing7 a voltage wave of the character illustrated at 10. Such voltage waveform has a rising portion which rises at a `decreasing rate, such portion having the reference numeral A; and such Waveform 10 has the vertical portion 10B which represents that the magnitude of the voltage changes from its maximum value to its minimum value in a very short time interval. The small horizontal portion 10C of the wave 10 represents a time interval during which the cathode beam may move from its maximum deflected position to its central original position O in Figure l. This time represented by the horizontal portion 10C represents the so-called yback time.

The diode rectifier tube 25 has its anode connected to the ungrounded terminal of condenser and its cathode connected to one terminal of resistance 26, the `other terminal of resistance 26 being connected to the anode of tube 13. It is observed that the serial circuit comprising tube 25 and resistance 26 is connected Vin shunt with the deflection coil 12 and serves to dampen `oscillations which otherwise may result in a large magnitude voltage during the flyback time, i. e., during the Vtime the magnetic flux originally produced by coil 12 collapses.

The voltage source 3) has its ungrounded terminal connected to the ungrounded terminal of condenser 15 through the resistance 32. This resistance 32 is effectively shunted by tube 34 during the flyback time or period; but, during the sweep period, the condenser 15 is charged through such resistance 32. For thispurpose, the tube 34, which is normally nonconducting, has its anode connected to one terminal of resistance 32 and its cathode connected to the other termina-l of resistance 32. The Icontrol grid of tube 34 is returned to ground through the serially connected resistances 36 and 37, the junction point of which is connected through condenser' 38 to the anode of tube 13.

During the sweep cycle, i. e., during the time when the voltage 10 rises, as indicated at 10A, the voltage on the anode of tube 13 is depressed to such an extent to cause the tube 34 to become nonconducting `so that, at this particular time, the condenser 15 which is supplying energy to the coil 12 is simultaneously being charged through resistance 32. At the end of the sweep, the voltage `on the anode of tube 13 suddenly rises and this rise in voltage is transferred through the condenser 38 to the control grid of tube 34 to thereby render such tube 34 conducting, and in such case, resistance 32 is effectively short-circuited and the-condenser 1'5 is charged through a circuit of relatively low resistance, whereby the voltage on condenser 15 may rise to its maximum value preparatory to the beginning of the next sweep. During such next sweep, tube 34 is rendered nonconducting and condenser 15 is being discharged at a controlled rate determined by the magnitude vof resistance 32 in its relationship to the magnitude of the capacitance 1S, i. e.,

by the time constant of the circuit comprising resistance 32 and condenser 15, substantially. This time constant is such that the change in voltage drop existing between the cathode and anode of tube 13 is much less than is otherwise the case when, for example, the positive terminal of voltage source 3% is -connected directly to one terminal tof the dellection coil 12.

While the particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects and, therefore, the aim in the appended claims is to cover al1 such changes and modifications as fall within the true spirit andscope of this invention.

We claim:

l. In a system of the character described, an inductance load, an amplifying discharge device having a control grid, a cathode and an anode, a source of recurrent sawtooth type of waves coupled to said device for controlling thc same, impedance means, a source of substantially continuous voltage connected in a serial circuit with said impedance means, load and the anode and cathode of said device, a condenser having one of its terminals connected to the junction point or" said load and impedance means and charged by said source through said impedance means, and means controlled by the voltage developed* on the anode of said device for effectively decreasing the magnitude of said impedance means in accordance with decreased current flow through said device, said impedance means having a finite impedance value at all times and providing a charging circuit for said condenser when and as said condenser is being discharged through said device.

2. In a system of the character described, a load, an amplifying discharge device having an anode and cathode, impedance means, a source of unidirectional voltage serially connected with said impedance means, load and the anode and cathode of said dischargedevice, said discharge device having a control element, a source of sawtooth type of waves coupled to said control element and controlling the current flow through said serial circuit, a condenser charged through said impedance means and serially connected with said device, and said load being coupled to said serial circuit and effective during the flyback time of each of said sawtooth waves for effectively decreasing the magnitude of-said impedance means in accordance with decreased current flow through said device, said impedance means having a finite impedance value at all times and providing a charging circuit for said condenser when and as said condenser is being discharged through said device.

3. In a sweep amplifying system of the character described, a source of voltage, an impedance means, a condenser charged by said source through said impedance means, a load serially connected with said condenser and supplied with energy therefrom, and means recurrently decreasing the magnitude of said impedance means in accordance with decreased current flow through said load, said impedance means having a finite impedance value at all times and providing a charging circuit for said condenser when and as said condenser is being discharged through said load.

4. In a system of the character described, a source of voltage, an impedance means, a condenser serially connected between said voltage source and said impedance means, a discharge device having a control element, a cathode and an anode, a load serially connected with said condenser andthe anode and cathode of said device in a serial circuit with said condenser supplying energy to said load and .said device, means coupled to said control element and producing a cyclical variation of current in said serial circuit, and means coupled to said serial circuit and sensitive to said variations for effectively decreasing the magnitude of said impedance ,means in accordance with decreased current flow through said device, said impedance means having a 'finite impedance value at all times and providing a charging circuit for said condenser when and as said condenser is being discharged through said device.

5. In a system of the character described, a source of continuous voltage, a resistance, an inductive load, a discharge device having an anode, a cathode and a control element, said source, resistance, load and device being connected in a first serial circuit, a condenser having one of its terminals connected to the junction point of said load and said resistance in a second serial circuit comprising said source, resistance and condenser, and in a third serial circuit comprising said condenser, load and device, a source of generally sawtooth Waves coupled to said control element, each of said sawtooth waves having a slowly rising portion and a quickly decaying portion which occur during the so-called flyback time, a second discharge device connected in parallel with said resistance and having a control grid, and a second condenser having one terminal connected to the anode of the rst-mentioned device and the other one of its terminals connected to said control grid for changing the resistance of said second device to thereby control the ow of charging current from the Erst-mentioned source to the first-mentioned condenser.

6. In a system of the character described, a first source of generally sawtooth waves, each of said waves having a slowly rising portion which is followed by a rapidly decaying portion, a second source of continuous voltage, a load, an amplifying device amplifying said sawtooth waves, resistance means, said second source, load, device and resistance means being connected in a serial circuit, a condenser coupled to said serial circuit and charged through said resistance means for supplying energy to said load, and means coupled to said serial circuit and sensitive to said rapidly decaying portion for decreasing the magnitude of said resistance means in accordance with decreased current flow through said device to thereby control the rate at which said condenser is charged, said impedance means having a finite impedance value at all times and providing a charging circuit for said condenser when and as said condenser is being discharged through said device.

7. In a system of the character described, a load supplied With sawtooth types of current waves, each of said waves having a slowly rising portion followed by a rapidly decaying portion, and said rising portion representing a current which ows at a decreasing rate comparable to an exponential logarithmic rate, a condenser coupled to said load for supplying said current, a source of Voltage for charging said condenser, impedance means connected between said source and condenser for controlling the charging of said condenser, and means coupled to said load and sensitive to said decaying portion for decreasing the magnitude of said impedance means in accordance with decreased current flow through said load, said impedance means having a finite impedance value at all times and providing a charging circuit for said condenser when and as said condenser discharges through said load.

8, In an amplifying system of the character described, a discharge device having a control element, a load connected with said device in a serial circuit supplied with sawtooth types of current waves, each of said waves having a slowly rising portion followed by a rapidly decaying portion, and said rising portion representing a current in said serial circuit which ows at a decreasing rate comparable to an exponential or logarithmic rate, means coupled to said control element for controlling said current at said rate, a condenser coupled to said serial circuit for supplying said current, a source of voltage for said condenser, impedance means connected between said source and said condenser for controlling the charging of said condenser, and means coupled to said load and sensitive to said decaying portion for decreasing the magnitude of said impedance means in accordance with decreased current ow through said device, said impedance means having a nite impedance value at all times and providing a charging circuit for said condenser when and as said condenser discharges through said device.

9. The system set forth in claim 3 in which said means for altering the magnitude of said impedance comprises an amplifying discharge device having a control grid, anode, and cathode with the anode and cathode serially connected with said condenser and said load, a source of recurrently appearing voltage applied to said control grid.

References Cited in the le of this patent UNITED STATES PATENTS 2,102,951 Hackenberg Dec. 21, 1937 2,221,665 Wilson Nov. 12, 1940 2,428,926 Bliss Oct. 14, 1947 2,455,283Y Valley Nov. 30, 1948 2,473,983 Wolf June 21, 1949 2,491,684 Munster et al Dec. 20, 1949 2,554,172 Custin May 22, 1951 

